The invention relates to methods of making nanocrystalline powder such as intermetallic powders.
Nanoparticles have been reportedly made from metals (e.g., Pd, Cu, intermetallics (e.g., Al52 Ti48)), semiconductors such as Si, metal carbonates such as ZnCO3, and metal oxides (e.g., SiO2, TiO2, Y2 O3, ZnO, MgO, Al2O3). See, for example, U.S. Pat. Nos. 5,580,655; 5,695,617; 5,770,022; 5,879,715; 5,891,548 and 5,962,132, the disclosures of which are hereby incorporated by reference. Previously, the production of nanoparticles has been reported by methods such as chemical synthesis, gas-phase synthesis, condensed phase synthesis, high speed deposition by ionized cluster beams, consolidation, high speed milling, deposition and sol-gel methods. These methods suffer from numerous drawbacks, including agglomeration, broad particle size distribution, or low volume production.
The most common method reported in the literature for the synthesis of intermetallic nanoparticles is mechanical ball milling. (Jartych E., et al., J. Phys. Condens. Matter, 10:4929 (1998); Jartych E., et al., Nanostructured Materials, 12:927 (1999); Amilis, X., et al., Nanostructured Materials 12:801 (1999); Perez R. J., et al., Nanostructured Materials, 7:565 (1996)). Jartych et al. report preparation of nanocrystalline powders of Fe-30 at. % Al, Fe-40 at. % Al and Fe-50 at. % Al by ball milling, all of which were found to possess strong ferromagnetic interactions. (Jartych E., et al., J. Phys. Condens. Matter, 10:4929 (1998); Jartych E., et al., Nanostructured Materials, 12:927 (1999)). However, the authors reported that even after 800 hours of milling time, small quantities of xcex1-Fe were still present in the samples as indicated by the hyperfine magnetic field distribution measurements. The presence of xcex1-Fe is believed to produce defects and high strain levels within the nanoparticles. Amilis and coworkers reported that the microhardness of nanoscale Fe-40Al at % alloy directly correlated with defect concentration. (Amilis, X., et al., Nanostructured Materials 12:801 (1999)). They reported possible media contamination during the process of ball milling, which resulted in the presence of low concentrations of SiO2 from the agate used for milling and presence of Fe3Al. Perez and coworkers reportedly synthesized nanoparticles of Fe-10 at. % Al using cryogenic milling at liquid nitrogen temperature. (Perez, R. J., et al., Nanostructured Materials, 7:565 (1996)). The thermal stability of these particles was found to be significantly higher than that of Fe nanoparticles produced under analogous conditions. The authors speculated that this increase in stability might be due to the formation of fine dispersoids of xcex3- Al2O3 or AlN, which would restrict the movement of the grain boundaries. In spite of the simplicity and efficiency of ball milling as a means by which nanoparticles of metallic alloys may be synthesized, there are some problems and limitations. For example, the microstructure of the milling products is very sensitive to the grinding conditions and may be unpredictably affected by unwanted contamination from the milling media and atmosphere. In addition, excessively long periods of milling time may be required to obtain particles smaller than 20 mn. (Amilis, X., et al., Nanostructured Materials 12:801 (1999); Perez R. J., et al., Nanostructured Materials, 7:565 (1996)).
In view of the state of the art, new methods of making intermetallic nanoparticles would therefore be desirable.
The present invention provides a simple and novel approach for synthesizing intermetallic nanoparticles using laser vaporization coupled with condensation from the vapor phase. The laser vaporization techniques provide several advantages over heating methods restricted by the temperature of the crucible. Among these advantages are the production of a high density vapor of any metal, the generation of a directional high-speed metal vapor from the solid target which can be useful for directional deposition of the particles, and the simultaneous or sequential evaporation of several different targets.
In one respect, the present invention provides a method of making intermetallic nanoparticles. The method comprises subjecting a starting material to laser energy so as to form a vapor and condensing the vapor so as to form intermetallic nanoparticles.
In one embodiment, the invention provides a method of producing intermetallic nanoparticles which employs laser vaporization with controlled condensation. This method allows control over the size, shape, and surface morphology of the nanoparticles that are produced.
Precise control of shape, size and surface morphology of materials at the nano scale level should serve as the underlying basis for building new high performance innovative materials that possess novel electronic, optical, magnetic, photochemical and catalytic properties. Such materials are essential for technological advances in photonics, quantum electronics, catalysis, nonlinear optics and information storage and processing.